The invention pertains to methods of electroless deposition of nickel over aluminum-containing materials and copper-containing materials, and in particular embodiments pertains to methods of forming under bump metallurgy (UBM) for subsequent solder bumps.
Conductive bumps are currently being utilized for connecting integrated circuitry associated with a semiconductor chip to other circuitry external of the integrated circuitry. Solder bumps are utilized in, for example, flip chip applications, multi-chip module applications, and chip scale packaging applications.
An exemplary solder bump construction is described with reference to FIG. 1. Specifically, FIG. 1 illustrates a fragment 10 of a semiconductor construction. Fragment 10 comprises a substrate 12 having a conductive layer 14 supported thereon. Substrate 12 can include a semiconductive material, such as, for example, monocrystalline silicon. To aid in interpretation of the claims that follow, the terms xe2x80x9csemiconductive substratexe2x80x9d and xe2x80x9csemiconductor substratexe2x80x9d are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure, including, but not limited to, the semiconductive substrates described above. Additionally, the terms xe2x80x9cmaterialxe2x80x9d and xe2x80x9clayerxe2x80x9d are to be understood to encompass pluralities of materials and layers, as well as single materials and layers, unless specifically stated otherwise.
Conductive material 14 can comprise a metallic material, such as, for example, one or more of aluminum and copper. In particular applications, conductive material 14 comprises aluminum or copper.
Substrate 12 can further include various circuit components (not shown), such as, for example, capacitors and transistors; and additionally can include insulative materials. Conductive material 14 can electrically connect with various of the circuit components associated with substrate 12.
An adhesion layer 16 is formed over conductive material 14. Adhesion layer 16 comprises, for example, titanium; and is utilized to improve adhesion of a masking material to the conductive material 14. For instance, if conductive material 14 comprises aluminum, a titanium-containing adhesion layer 16 can improve adhesion of various masking materials (such as materials comprising polyamide or BCB) over the aluminum.
A masking layer 18 is formed over adhesion layer 16. Masking layer 18 can comprise, for example, polyamide or BCB materials (with BCB materials being materials derived from bisbenzocyclobutane chemistry). Masking layer 18 can be patterned by providing photoresist (not shown) over the masking layer, using photolithographic methods to pattern the photoresist, and subsequently transferring a pattern from the photoresist to layer 18 with an appropriate etch.
The patterning of masking layer 18 forms an opening 20 extending through patterned masking layer 18. Opening 20 is shown extending through adhesion layer 16 and to conductive material 14. The shown opening 20 can be formed by first patterning masking layer 18 to expose a portion of adhesion layer 16, and subsequently removing the exposed portion of adhesion layer 16 to extend the opening entirely through layer 16 and to conductive material 14.
A nickel-containing layer 22 is formed within opening 20 and over conductive material 14. Nickel-containing layer 22 can be formed by, for example, electroless deposition, which is also referred to as autocatalytic electrolytic deposition (AED). Prior to the electroless deposition of nickel-containing layer 22, aluminum-containing material 14 within opening 20 is cleaned, and then subjected to activation with a zinc-containing solution. Such activation forms a thin zinc-containing material (not shown) over aluminum-containing layer 14. Subsequently, nickel-containing layer 22 is formed on the thin zinc-containing material by reduction of nickel from a nickel salt. An exemplary chemistry for electroless deposition of zinc comprises reactions I and II.
NiSO4+2exe2x88x92xe2x86x92Ni+SO42xe2x88x92xe2x80x83xe2x80x83I. 
3H++(NH4)2H3P2O4xe2x86x922NH4++2H3PO2xe2x88x92+2exe2x88x92xe2x80x83xe2x80x83II. 
After formation of nickel-containing layer 22, a gold-containing layer 24 is formed over nickel-containing layer 22. Gold-containing layer 24 can be formed by electroless deposition utilizing, for example, gold sulfide as a source of gold. The gold can be used as a wetting agent for subsequent solder formation.
It is noted that nickel-containing layer 22 can consist of, or consist essentially of, nickel; and that gold-containing layer 24 can consist of, or consist essentially of, gold.
A solder bump 26 is formed over gold-containing layer 24. Solder bump 26 can comprise, for example, a tin and/or lead-based solder.
The methodology described above is typical of what would be utilized for forming a solder bump over a layer 14 which comprises predominantly aluminum (i.e, comprises more than 50 atomic percent aluminum), consists essentially of aluminum, or consists of aluminum. If layer 14 comprises copper, the methodology will typically be somewhat different. For instance, adhesion layer 16 will typically be eliminated, and masking layer 18 will typically comprise BCB materials. Further, a layer 14 which comprises predominantly copper, consists essentially of copper, or consists of copper, will typically be exposed to an activation solution which comprises palladium, instead of zinc, to form a thin layer of palladium (not shown) over layer 14. Subsequently, nickel-containing layer 22 will be formed over the thin layer of palladium utilizing the electroless chemistry described previously, and gold layer 24 will be formed over nickel-containing layer 22 utilizing electroless chemistry. Finally, solder bump 26 can be formed over gold layer 24.
It would be desirable to develop improved methods for forming electrical connections from solder bumps to conductive materials associated with semiconductor substrates.
In one aspect, the invention encompasses a method of electroless deposition of nickel over an aluminum-containing material. A mass is formed over the aluminum-containing material, with the mass predominantly comprising a metal other than aluminum. The mass is exposed to palladium, and subsequently nickel is electroless deposited over the mass.
In another aspect, the invention encompasses a method of electroless deposition of nickel over aluminum-containing materials and copper-containing materials. The aluminum-containing materials and copper-containing materials are both exposed to palladium-containing solutions prior to electroless deposition of nickel over the aluminum-containing materials and copper-containing materials.
In another aspect, the invention encompasses a method of forming a solder bump over a first material. The first material comprises one or both of aluminum and copper material. A titanium-containing material is formed over the first material, and a patterned mask is formed over the titanium-containing material. The patterned mask comprises polyamide and/or a BCB material, and has an opening extending therethrough to the titanium-containing material to expose a portion of the titanium-containing material. A palladium-containing material is formed on the exposed portion of the titanium-containing material. A nickel-containing material is electroless deposited on the palladium-containing material, and a gold-containing material is formed on the nickel-containing material. Finally, a solder bump is formed over the gold-containing material.